ABP中GetAll查询出来的IQueryable类型数据，扩展进行排序
基于IEnumerable<T>接口的LINQ to Object扩展函数运行开发人员提供Func<T, TResult>类型的委托实现排序，看一个简单的例子：
public class Person
{
public Person() : this(Guid.NewGuid().ToString("N"), DateTime.Now) { }
public Person(String name, DateTime birth)
{
this.Name = name;
this.Birth = birth;
}
public String Name { get; set; }
public DateTime Birth { get; set; }
}
IEnumerable<Person> persons = new Person[] { new Person(), new Person(), new Person() };
IOrderedEnumerable<Person> persons2 = persons.OrderBy(p => p.Name);
IOrderedEnumerable<Person> persons3 = persons.OrderBy(delegate(Person p) { return p.Name; });
IOrderedEnumerable<Person> persons4 = persons.OrderBy(p => p.Name, StringComparer.CurrentCultureIgnoreCase);
上面类型中的属性是已知并且可被推导的，如果属性只有一个名称怎么才能够依然可以排序呢？比如下面的写法：
IOrderedEnumerable<Person> persons = persons.OrderBy("Name");
IQueryable<T>接口可以将查询解析为表达式树，我们可以看到IQueryable<T>的OrderBy、OrderByDescending扩展函数分别相比IEnumerable<T>多了两个接受Expression<Func<T, TResult>>的函数：
public static IOrderedQueryable<TSource> OrderBy<TSource, TKey>(this IQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector);
public static IOrderedQueryable<TSource> OrderBy<TSource, TKey>(this IQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector, IComparer<TKey> comparer);
public static IOrderedQueryable<TSource> OrderByDescending<TSource, TKey>(this IQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector);
public static IOrderedQueryable<TSource> OrderByDescending<TSource, TKey>(this IQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector, IComparer<TKey> comparer);
也就说我们可以动态构建Lambda表达式来实现动态调用OrderBy、OrderByDescending函数。看一个例子：
1 Type type = typeof(T);
2 ParameterExpression arg = Expression.Parameter(type, "p");
3 PropertyInfo property = type.GetProperty(propertyName);
4 Expression expr = Expression.Property(arg, property);
5 Type delegateType = typeof(Func<,>).MakeGenericType(typeof(T), property.PropertyType);
6 LambdaExpression lambda = Expression.Lambda(delegateType, expr, arg);
arg就是传递的参数类型，也就是Func<T, TResult>的T类型。通过Expression.Property创建了函数执行体，并定义访问传递参数的某一个属性。最后创建出表达式，等同于p => p.属性。最后找到Queryable静态类型中定义的OrderBy、OrderByDescending函数动态调用就可以实现传递属性名称实现排序。
1 /// <summary>
2 /// 排序的扩展类
3 /// </summary>
4 public static class QueryableOrderEx
5 {
6
7 /// <summary>
8 /// 顺序排序
9 /// </summary>
10 /// <typeparam name="T"></typeparam>
11 /// <param name="source"></param>
12 /// <param name="propertyName"></param>
13 /// <returns></returns>
14 public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> source, String propertyName)
15 {
16 return InternalOrder<T>(source, propertyName, "OrderBy");
17 }
18
19
20 /// <summary>
21 /// 倒序排序
22 /// </summary>
23 /// <typeparam name="T"></typeparam>
24 /// <param name="source"></param>
25 /// <param name="propertyName"></param>
26 /// <returns></returns>
27 public static IOrderedQueryable<T> OrderByDescending<T>(this IQueryable<T> source, String propertyName)
28 {
29 return InternalOrder<T>(source, propertyName, "OrderByDescending");
30 }
31
32
33 /// <summary>
34 ///
35 /// </summary>
36 /// <typeparam name="T"></typeparam>
37 /// <param name="source"></param>
38 /// <param name="propertyName"></param>
39 /// <returns></returns>
40 public static IOrderedQueryable<T> ThenBy<T>(this IOrderedQueryable<T> source, String propertyName)
41 {
42 return InternalOrder<T>(source, propertyName, "ThenBy");
43 }
44
45 /// <summary>
46 ///
47 /// </summary>
48 /// <typeparam name="T"></typeparam>
49 /// <param name="source"></param>
50 /// <param name="propertyName"></param>
51 /// <returns></returns>
52 public static IOrderedQueryable<T> ThenByDescending<T>(this IOrderedQueryable<T> source, String propertyName)
53 {
54 return InternalOrder<T>(source, propertyName, "ThenByDescending");
55 }
56
57
58 /// <summary>
59 ///
60 /// </summary>
61 /// <typeparam name="T"></typeparam>
62 /// <param name="source"></param>
63 /// <param name="propertyName"></param>
64 /// <param name="methodName"></param>
65 /// <returns></returns>
66 private static IOrderedQueryable<T> InternalOrder<T>(IQueryable<T> source, String propertyName, String methodName)
67 {
68 Type type = typeof(T);
69 ParameterExpression arg = Expression.Parameter(type, "p");
70 PropertyInfo property = type.GetProperty(propertyName);
71 Expression expr = Expression.Property(arg, property);
72 Type delegateType = typeof(Func<,>).MakeGenericType(typeof(T), property.PropertyType);
73 LambdaExpression lambda = Expression.Lambda(delegateType, expr, arg);
74
75 return ((IOrderedQueryable<T>)(typeof(Queryable).GetMethods().Single(
76 p => String.Equals(p.Name, methodName, StringComparison.Ordinal)
77 && p.IsGenericMethodDefinition
78 && p.GetGenericArguments().Length == 2
79 && p.GetParameters().Length == 2)
80 .MakeGenericMethod(typeof(T), property.PropertyType)
81 .Invoke(null, new Object[] { source, lambda })));
82 }
83 }
1 IEnumerable<Person> persons = new Person[] { new Person(), new Person(), new Person() };
2 IOrderedQueryable<Person> persons2 = persons.AsQueryable().OrderBy("Name");
3 IOrderedQueryable<Person> persons3 = persons.AsQueryable().OrderByDescending("Name");
1 //ABP项目中的使用例子，参考STK项目
query = !string.IsNullOrEmpty(input.Sorting) 2 ? query = (input.SortBy == SortByEnum.ASC ? QueryableOrderEx.OrderBy<STKForm.STKFormHead>(query, input.Sorting) : QueryableOrderEx.OrderByDescending<STKForm.STKFormHead>(query, input.Sorting)) 3 : query.OrderByDescending(t => t.CreationTime);
